1. Field of the Invention
This invention relates to a silver halide photographic light-sensitive material and, more particularly, to a silver halide photographic light-sensitive material providing photographic characteristics of extremely high contrast negative gradation.
2. Description of the Prior Art
U.S. Pat. No. 2,419,975 teaches that high contrast negative photographic characteristics can be obtained by adding a hydrazine compound to a silver halide photographic emulsion. This patent describes that extremely high contrast photographic characteristics, such as a gamma (.gamma.) of more than 10, are obtained by adding a hydrazine compound to a silver bromochloride emulsion and developing with a developer having a pH value as high as 12.8. However, strongly alkaline developers having pH value near 13 are susceptible to oxidation by air and are therefore too unstable to be stored for a long period of time.
Super-high contrast photographic characteristics of more than 10 in gamma are extremely useful for the photographic reproduction of images with continuous gradation employing a dot image-forming process which is useful for making printing plates or for reproduction of line images, irrespective of whether the images are negative or positive. For the purpose of obtaining such photographic characteristics, a silver chlorobromide emulsion containing more than 50 mol% and preferably more than 75 mol% silver chloride has been used and developed with a hydroquinone-containing developer having an extremely reduced concentration of effective sulfite ion (usually 0.1 mol/l or less). However, such developer is very unstable due to its low sulfite ion concentration and cannot be stored longer than three days.
In addition, the above-described processes all require a silver chlorobromide emulsion containing silver chloride in a comparatively high content and hence high sensitivity cannot be obtained. Thus, it has been eagerly desired to obtain super-high contrast photographic characteristics useful for the reproduction of dot images or line images using a highly sensitive emulsion and a stable developer.
We have previously disclosed silver halide photographic emulsions permitting extremely high contrast negative photographic characteristics using a stable developer in Japanese Patent Application (OPI) Nos. 16623/78, 20921/78 (corresponding to U.S. Patent Application Ser. No. 967,541 filed on Dec. 7, 1978), 20922/78, etc. (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".) However, the acylhydrazine compounds used therein have proved to possess some defects. One is that they undergo serious changes in sensitivity and gradation when the degree of stirring of the developer varies. Light-sensitive materials for use in printing are processed using an automatic developing machine or manual development (dish development). Usually, stirring conditions greatly differ depending upon the developing process and, in addition, stirring methods or stirring strength differ depending upon the type of automatic developing machine. Thus, differences in sensitivity and gradation result depending upon the manner in which the photographic materials are processed. Further, even in the same automatic developing machine, the stirring of the developer is not always uniform but varies from place to place within the developing machine and often results in uneven development when developing large sized film. Therefore, it has been strongly desired to obtain super-high contrast photographic light-sensitive materials which exhibit less variation in sensitivity and gradation and free from uneven development even when the developer stirring conditions vary and which are useful for the reproduction of dot images or line images.